The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Vehicles include an internal combustion engine that generates drive torque. An intake valve is selectively opened to draw air into a cylinder of the engine. The air mixes with fuel to form an air/fuel mixture. The air/fuel mixture is combusted within the cylinder. An exhaust valve is selectively opened to allow the exhaust gas resulting from combustion to exit the cylinder.
One or more rotating camshafts regulate the opening and closing of the intake and/or exhaust valves. The camshafts include cam lobes that are fixed to and rotate with the camshafts. The geometric profile of a cam lobe determines a valve opening schedule. More specifically, the geometric profile of a cam lobe generally controls the period that the valve is open (duration) and the amount or distance (lift) that the valve opens.
Variable valve actuation (VVA), also called variable valve lift (VVL) improves fuel economy, engine efficiency, and/or performance by modifying valve lift and duration as a function of engine operating conditions. Two-step VVA systems include VVL mechanisms, such as hydraulically-controlled, switchable roller finger followers (SRFFs). A SRFF associated with a valve (e.g., the intake or exhaust valves) allows the valve to be lifted in two discrete modes: a low lift mode and a high lift mode. The valve lift associated with the high lift mode is greater than the valve lift associated with the low lift mode.